You can preorder the PC Version of SFiv with a discounted price from amazon here:
SFIV + Madcatz sf4 pad bundle:
SFIV pc version standalone (discounted price):
The Pc version comes with the extra shader option that is not available on consoles. sven even went ahead and claimed that the PC version is the best port com[pared to the 360 and ps3 version.
Sven: "The PC version is the best of the lot on the right hardware (for all of the reasons you'd called out above). I hope that PC enthusiasts take a shine to it and support it. It deserves it. "
Let's hope that this is true as i will be getting the PC version as well.
Make sure that your pc will run SF4 before cashing the money for it by downloading and running the benchmark tool released by Capcom few weeks ago.
source: Examiner and Cap Unity